Multiple radios, 1 speaker/master volume

[phyberoptics]

Originally Posted by trooperdude

I can do the same thing for $250 less with a $100 Behringer mixer board
and some Royal DB25 PADS into the unbalanced mic inputs.

In fact I do. 12 separate channels (radios) with full dynamic range
control, output into amplified stereo speakers.

Look at some of the pro audio gear out there. There are several unpowered pads
that would work quite well for mobile audio use.

In fact a friend of mine has 4 radios input into his stereo aux input in the car, all with levels controlled with pots on the (really small) dash-mounted device.

Do you have a link to the mobile device you mention here?

[Halfpint]

Lessee.... Hopefully I can get this drawing to upload. {WAN GRIN!} *If* it does then maybe what I suggested might be a bit clearer. I didn't include the "L-pad" in it but, all one has to do is insert it between the speaker and the transformer following the instructions that usually come with them, the "L-pad". Whole project, including the "L-pad" should probably only cost somewhere around $10 or so and that is using a transformer and "L-pad" rated for around 5watts or so. One should be able to hold all the parts for a pair of radios, except possibly the wire, in one hand.

Just an `Olde Fart's' 2¢ worth. {GRIN!}

[frankh]

check this out http://www.behringer.com/MX400/index.cfm?lang=ENG

[K8PBX]

Originally Posted by frankh

check this out http://www.behringer.com/MX400/index.cfm?lang=ENG

That's a good find! Looks pretty slick and runs on 12vdc too. MSRP is $29.99

[Halfpint]

Originally Posted by frankh

check this out http://www.behringer.com/MX400/index.cfm?lang=ENG

After actually taking the time to check out the specs on this I'd, quite frankly, be *very* surprised if it would even begin to work with speaker level signals. Mixers, by and large, are devices that are intend for use with what are known as *line level* signals which are usually measured in MilliVolts, IE: 0.001V for instance, not Volts. Speaker level signals are measured in Volts. Also, even in HH scanners and other radios the output usually needs to have some power, IE: Watts, to be able to drive the speaker load, usually somewhere around 4 - 32 Ohms, whilst the output of mixers seldom are called upon to deal with loads of less than around 1,000 Ohms and as high as 1,000,000 Ohms which means that their output usually can be specified at around 0.000,010 Watts *if* it is even specified at all. To expect a mixer to have enough `Moxie' to adequately drive a speaker is truly wishfull thinking. There *may* be instances of it happening but I wouldn't give a `snowball's chance in someplace warm that rhymes with swell' of the little OpAmp, or whatever, that is doing the buffering of the output to last very long doing so. On top of that the mismatch on the inputs is going to horrendous. One will have to have the volume coontrol of the radio turned down so low that there might not even be a chance that it will actually be of any real use. (The best example I can think of immediately is trying to record from the ear, or head, phone out of a radio into the microphone input of a tape recorder. Anyone who has tried this knows that whilst it can sometimes be done the usual result is a lot of distorted, sometimes to the point of basically being garbage, sounds on the tape and not much else. The same thing, but to a slightly lesser extent, happens if one tries using the Aux input, if it has one, on the recorder only then one might actually be able to turn down the volume of the radio and might actually get something a tad bit more intelligible on the tape.)

Now... *if* the radio just *happens* to have an `Aux' or `Tape' output the input of the mixer most likely won't end up being overloaded and there may not be that particular case of distortion to deal with. But, that still leaves the problem of driving the speaker on the output to a listenable level. *IF* one just *has* to have a mixer then the best bet would be to get a cheap PA Amp/Mixer unit and input the radios into it. (This is supposing that the radios have said `Aux'/`Tape' output connection.) However, trying to run a speaker output into even one of those type units will still lead to a distorted output. (One *could* get lucky and actually find the point within the first few degress of volume control travel where the signal was acceptable to the input. But, I wouldn't want to have to always be tweaking the volume controls of different units all the time just to keep within that range especially if said volume control also happens to be the Off/On switch. Yeah, the input control on the mixer will help a bit but, it is just another place where trouble can rear it's ugly head.)

All of the preceding is basically why there are those `fancy?' units like the New Communications Solutions NCS-C230 Multi-RX unit are out there. Not only do they allow one to use multiple radios with one or two speakers but they also handle all the assorted variables attendant with doing so. (Yeah, I *know* that the NCS-C230 Multi-RX unit works with a pair of speakers! It just happens to be the one *I* am the most `familiar' with. While I cannot give you the maker(s) and/or model(s) of units that are for only one speaker a quick search can probably locate at least one or two that do.) The circuit(s) that I provided will also handle hooking up a pair or two of radios *and* will do it a *lot* cheaper. One *may* have to do a bit of searching to find the transformer, and maybe even the "L-Pad", but, one doesn't have to provide any power to the circuit, except for that already provided by the radios, and it can all be installed within most, if not pretty much all depending upon physical size, of the auxillary speaker enclosures most of us may use. (My specifying a 5W transformer was just an example. One could probably get by with one spec'd for 1W and get by quite well. Using one spec'd for 1W might even make the circuit mountable within some of the really small speaker units. [I've got a little round speaker that I know that I'd probably have to go with a circuitboard mountable, .5 - .75W spec'd, transformer *if* I wanted to make the attempt and even then it would probably be impossible. However, *if* I were to just go up to one that had a square or rectangular case and same sized speaker it would fit. As long as I didn't try to go for a volume level that could be heard in the next car over at a stoplight with windows down on both cars I could handle a pair of scanners putting out some fairly decent volume and not worry about `cooking' the transformer.] Since we would be dealing with basically just `voice' and not `music' we don't have to worry as much about `power handling' as we might usually do. [It's a `duty-cycle' thing. `Voice', like what we are dealing with in this situtation, makes less of a call for full power over time than does `music'. This gives the transformer time to cool down between power peaks. This is also why the audio power amps in most two-way radios aren't nearly as powerfull as those in even a lot of mid to cheap portable AM/FM/FM Stereo radios out there and are sometimes small surface mounted devices with only the copper on the circuitboard as heatsinking. (There are some other `tricks' they use, too. {GRIN!} In the 40 or so years I've been in the `industry' I've seen some Lulus! I'll also admit that I have used a few of them myself in things I've designed or helped design.)]) This is an instance of where cheap and simple is definitely the way to go and why I am advocating such.

Just an `Olde Fart's' 2¢ worth. {CHORTLE!}

[frankh]

I guess I should have elaborated, the mixer should be feed with your line out from your scanner and into a set of amplified speakers or something like the RS dsp 40. I got the idea for this from RR (do a search for beringer on RR). Beringer products are well known for their high quality, and I wouldn't be surprised if it would work with speaker output. This is a much less costly solution then the NCS unit.

[jonny290]

Originally Posted by Halfpint

After actually taking the time to check out the specs on this I'd, quite frankly, be *very* surprised if it would even begin to work with speaker level signals. Mixers, by and large, are devices that are intend for use with what are known as *line level* signals which are usually measured in MilliVolts, IE: 0.001V for instance, not Volts. Speaker level signals are measured in Volts. Also, even in HH scanners and other radios the output usually needs to have some power, IE: Watts, to be able to drive the speaker load, usually somewhere around 4 - 32 Ohms, whilst the output of mixers seldom are called upon to deal with loads of less than around 1,000 Ohms and as high as 1,000,000 Ohms which means that their output usually can be specified at around 0.000,010 Watts *if* it is even specified at all. In the 40 or so years I've been in the `industry' I've seen some Lulus! I'll also admit that I have used a few of them myself in things I've designed or helped design.)]) This is an instance of where cheap and simple is definitely the way to go and why I am advocating such.

Just an `Olde Fart's' 2¢ worth. {CHORTLE!}

that mixer has max input of +16 dBu
i'm curious what part of the specs led you to believe that mixer would get overloaded


it'll be absolutely fine with that.


run a 5 w audio amp inline with it or use a powered external speaker like you probably would anyways, it'll play fine with line out

I run external speaker lines into my Behringer 2442FX board all day long, set the volume at 10 o'clock, it plays exactly like my line level audio gear.

If you guys are really serious about this project i'll whip up a DIY in/out mixer that will be scalable, I just have to do a little bit more research with audio switching transistors and i'll be ready to begin the project.

[benjaminfs733]

Here is a related question. (I have asked this before [in a different forum] but I am still looking for options). I have a scanner (996) in my cruiser with an external speaker high to the rear of the seat. I have a radio with an external speaker under the dash. The problem comes when I transmit sometimes the scanner volume is too loud and causes feedback or is just annoying. What I am looking for is some sort of auto mute or a method to mute my scanner when I take the mic off the clip.

datainmotion gave me this idea. But surely there is something out there that is manufactured professional of this type job. Don't lots of agencies have multiple radios that would need to be muted some way when talking on another?

"Route the scanner's audio out wire past the mic clip and have the "high" side connect through a small switch (http://www.radioshack.com/product/in...58.2032230.203 2278&pg=3&allCount=69&fbn=Price%2FUnder+%243.99&fb c=1&fr=StorePrice%2FRSK%2F00000000%2F00000399&pare ntPage=family) installed behind/under the clip."

Thanks for any thoughts.

[jonny290]

my proposed box will have just such a circuit, soft PTT control with user selectable muting matrix. doing research on switch ic's now

What you really want to do though is to ground the antenna input when you're transmitting - that saves the front end of your scanner

[topcop1833]

benjaminfs733, forgive me if i have not understood your question correctly, but if you are getting feed back from a channel you are talking on in your car, why not simply not scan that particular freq? you are already listening to it via two-way radio, i wouldnt see a need to scan it as well via another device.

[frankh]

Originally Posted by benjaminfs733

Here is a related question. (I have asked this before [in a different forum] but I am still looking for options). I have a scanner (996) in my cruiser with an external speaker high to the rear of the seat. I have a radio with an external speaker under the dash. The problem comes when I transmit sometimes the scanner volume is too loud and causes feedback or is just annoying. What I am looking for is some sort of auto mute or a method to mute my scanner when I take the mic off the clip.

datainmotion gave me this idea. But surely there is something out there that is manufactured professional of this type job. Don't lots of agencies have multiple radios that would need to be muted some way when talking on another?

"Route the scanner's audio out wire past the mic clip and have the "high" side connect through a small switch (http://www.radioshack.com/product/in...58.2032230.203 2278&pg=3&allCount=69&fbn=Price%2FUnder+%243.99&fb c=1&fr=StorePrice%2FRSK%2F00000000%2F00000399&pare ntPage=family) installed behind/under the clip."

Thanks for any thoughts.

For what its worth, scannermaster used to make a plug in for the 780 that muted audio when you transmitted, maybe they can help you out with the 996.

[benjaminfs733]

Thanks for the info. I have been told that the auto mute for the 780 will not work on the 996. And sometimes it is a different system, state police, in the background of my mic. and sometimes my scanner when I key up will broadcast the freq. I am on on the wrong channel causing feedback, ie; I transmit on PD1, 1200 and scanner displays and sends out my transmission on say ID 1136 (fire dispatch).

Thanks again, and sorry to take the thread in a different direction that intended.

[kskarma]

This may provide an idea for some.... Many years ago, I worked at a TV station where there were several banks of speakers in the news room...about 6 speakers in each of the banks, each fed by a separate monitor...no scanner...just separate feeds to each speaker. Each speaker had its own volume control so the news people could turn up the ones they were most interested in. There were many complaints from the news folks that it was difficult for them to tell which agency was 'active' and they wasted a lot of time trying to 'zero in' on which ever one had the 'hot' news story going on. The Engineering Manager came up with a simple idea that solved that problem for just a few $$$$...! What he had us do was to wire a small audio output transformer backwards across the voice coil of the speakers...these were the normal HI-Z to 8 ohm transformers...with the 8 ohm side in parallel with the voice coil...and...(here is the GOOD part)..the HI-Z side was connected to a neon bulb mounted on the front of each speaker..!! Since the neon bulb took NO power to light up and would glow at about 60 volts...it worked great. When any of the agencies would transmit, the little neon bulbs would flicker in step with the dispatchers voices and it was very simple to identify which speaker/agency was active....even if several were transmitting at the same time, it was easy to 'read' the pattern of the bulbs...and know exactly which dispatcher..or agency was on the air... The system worked great and everyone was very pleased with it. Some variation of this might be useful for readers of this forum....

[Canvoodoo]

Originally Posted by Halfpint

What we came up with was an audio transformer that had an 8ohm input and 2 8ohm outputs. We simply reversed the connections, made the outputs inputs and the input the output.

This sounds like it would neatly solve an installation issue for me. I know that this is a very olde post, but does anyone have any idea where I could find such a transformer? I'm assuming that the transformer described is 8 ohm on one side and 16 ohm CT (or 2x 8 ohm) on the other. Have I gotten this right, and does anyone know where I would be able to find such an animal?